A vacuum is space that contains no matter. Outer space is a vacuum, more or less. We can create artificial vacuums here on earth. The strange thing about a vacuum is that sound cannot travel through it. So, if something big out in space explodes, in a supernova, you can see it, but you will never hear it. If you’re in space, and a bomb goes off near you, you may feel the heat wash over you, but you won’t hear it.

The reason that sound can’t travel in a vacuum is that there aren’t any particles to carry the wave. Sound waves are longitudinal waves that must have a medium to travel through. They cannot transfer energy from particle to particle because they are spaced too far apart, and the energy cannot jump from particle to particle.

Whenever you see a movie that takes place in space, listen to see if they’re following this law of physics. Much of the time, if there’s an explosion, they add sound effects, when in reality it’d be silent. Take the newer Star Trek movie, for example. When people are pulled out into space after part of the ship was destroyed, everything was silent. That is how it should be. Next time you’re watching a space movie, listen intently to your sub and speakers, and see if the filmmakers got it right.

Probably the coolest way to see sound waves is with fire. In 1905, German physicist Heinrich Rubens invented the Rubens’ tube, or the standing wave flame tube. The Rubens’ tube demonstrates acoustic standing waves through fire.

The Ruben’s tube is a length of pipe that has evenly-spaced holes along the top and is sealed at both ends. One seal is attached to a speaker or frequency generator while the other seal is attached to a propane tank. The tube is filled with gas, and the gas that comes out of the holes is lit on fire. You can now see the sound waves, etched into the air by way of fire.

If a constant frequency is used, then the inside of the tube will have a standing wave, and will create points with oscillating pressure and points with constant pressure. The flames will be lower at the points of oscillating pressure because less gas will escape through the holes in the tube. Naturally, the flames will be higher at the points of constant pressure.

Having a standing wave is cool, but not nearly as much fun as playing music into the Rubens’ tube. Take a look, it’s really quite enjoyable:

The Voices:

AudiOdysseus

My name is AudiOdysseus. Admittedly, I would never describe myself as a hero of any kind and I tend to get seasick in open water. But I love adventure. There is nothing I appreciate more than exploring new territories and gathering information about the world around me. Those are also the types of posts you can expect from me. I’ll be writing mostly about new gadgets, emerging trends, and my work-related travels to other lands.

Penny Lane

I'm passionate about music, a lover of pop-culture, a runner with a mad sweet tooth and an addiction to coffee. Read my musings about life, movie soundtracks and live concerts. If you see me on the freeway I am most likely singing very loudly in my car. Honk and say hi!

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Ace of Bass

Born and bred in the Silicon Valley, I have an innate passion for all things technology. I'll post about home theater, quality sound, apps and much more. If I bump into you, its probably because I'm looking at my iPhone. Sorry!

Echo

Owner of vPulse and vFree and curious for the ventures of Velodyne Acoustics, I will be exploring our headphones and what we do next. Stay tuned as I share what I find.

Audio8master

Born and raised in Silicon Valley, I am a student at San Jose State University and Marketing intern at Velodyne Acoustics. I am an avid San Jose Sharks hockey fan and San Francisco 49ers football fan. When I'm not watching sports, I'm listening to music and thinking deep thoughts about sound.